1. Field of the Invention
This invention relates to a self-assembled chromogenic receptor in which the chromophore is an intrinsic part of the binding site and the optical response is dramatic and reversible. The receptor is based on a phenanthroline derivative and the addition of Cu[CH.sub.3 CN].sub.4.sup.+ BF.sub.4.sup.- leads to a remarkable self-assembly of a metal templated receptor containing binding sites for medically important substrates. This invention also relates to a method of employing the chromogenic receptors in delineation of medically important substrates in biological solutions.
2. Background Information
The development of synthetic receptors for neutral molecules has been an area of active research in recent years. These systems include complexes stabilized by hydrophobic interactions (e.g., cyclophanes), #--# stacking (e.g., "molecular tweezers"), and hydrogen bonding. Garcia-Tellado et al., J. Chem. Soc., Chem. Commun. 1991, 1761-1763. The study of these complexes has contributed to an understanding of the relative strengths of the various forces involved in binding and a growing knowledge of the subtle design changes that can be used to effect substrate selectivity, including stereoselectivity. Diederich, Cyclophanes; The Royal Society of Chemistry: Cambridge, UK, 1991; Hamilton, A. D. In Bioorganic Chemistry Frontiers; H. Dugas, Ed.; Springer-Verlag: Berlin, 1991; Vol. 2; pp. 117-174; Rebek, J. J. Acc. Chem. Res. 1990, 23, 399; Zimmerman et al., J. Org. Chem. 1990, 55, 4789-4791; Tanaka et al., J. Am. Chem. Soc. 1990, 112, 2807-2808; Garcia-Tellado et al., J. Am. Chem. Soc. 1990, 112, 7393-7394; Kelly-Rowley et al., J. Am. Chem. Soc. 1991, 113, 9687-9688; Chapman et al., J. Am. Chem. Soc. 1989, 111, 3075-3077.
The success of these systems largely depends on the skills of the synthetic chemist, who must properly orient the binding groups of the receptor to complement those of the intended substrate. While there have been many notable successes using this approach, an alternative method can be envisioned in which a receptor self-assembles from smaller constituents. This strategy is commonly seen in biological receptors. For example, the dimerization of HIV protease is a prerequisite for its biological activity. Blundell et al., Trends Biochem. Sci. 1990, 425-430; Zhang et al., J. Biol. Chem. 1991, 266, 15591-15594. Self assembly is defined here as two or more separate molecules coming together through noncovalent interactions to form the active receptor. Self-assembled receptors offer several advantages over traditional receptors. Smaller subunits are easier to synthesize than fully elaborated receptors. In addition, careful control over the self assembly process can potentially lead to a large number of different receptors from just a few subunits. Moreover, self assembly has the potential to provide access to very large and complicated receptors for the recognition of large structures (e.g., protein surfaces and DNA). However, to date there have been only limited reports pertaining to the self assembly of synthetic receptors. Drain et al., J. Chem. Soc., Chem. Commun. 1993, 243-245; Fujimoto et al., Tetrahedron Lett. 1994, 35, 2915-2918.
Ligand coordination to metals has been used extensively to assemble elaborate structures, including helices (Kramer et al., Proc. Natl. Acad. Sci., 1993, 90, 5394-5398; Ziessel et al., Angew. Chem. Inc. Ed. Engl., 1993, 32, 87), multicomponent photochemical devices, and catenanes (Dietrich-Buchecker et al., Tetrahedron Lett., 1983, 24, 5095-5098). In addition, receptors have been constructed in which metal coordination to a metal binding site on the receptor produces an allosteric effect on binding at another site. Deng et al., J. Am. Chem. Soc., 1994, 116, 4567-4572; Inouye et al., J. Am. Chem. Soc., 1993, 115, 8091-8095; Murakami et al., J. Chem. Soc., Chem. Commun., 1993, 1533-1535. However, the use of coordination sites of a transition metal as a template for the self-assembly of a receptor has not received attention.
Therefore, in spite of the prior art disclosures, there remains a very real and substantial need for a self-assembled chromogenic metal chelate receptor with open coordination sites that can be used for metal ion catalyzed reactions on medically important bound substrates. There also is a need for employing a sensitive probe for determination in biological solutions of medically important substrates such as carbohydrates (glucose), steroids (cholesterol), amino acids (lysine), dicarboxylic acids (glutaric acid), and pyrophosphates (adenosine diphosphate).